Breast cancer survivors comprise an increasingly large proportion of the population with over 2 million alive in the United States. Cardiovascular disease (CVD) is the leading cause of death among women in the general population over age 50 and appears to be one of the leading causes of death among older women with early stage breast cancer. Emerging evidence suggests that women with breast cancer might be at higher baseline CVD risk than the general population and that breast cancer treatment might further increase CVD risk. However, the exact magnitude of CVD risk in women with breast cancer is not clear. Using the Nurses Health Study (NHS), a prospective cohort study of 121,700 registered nurses aged 30-55 at baseline in 1976 with more than 30 years of follow-up, we will examine the competing causes of morbidity and mortality among women with early stage breast cancer age 50 or older and also compare them to women age 50 or older without a personal history of breast cancer. With detailed data on breast cancer characteristics, lifestyle risk factors, and health behaviors, the NHS provides a unique resource to precisely estimate the burden of chronic disease risk on survival and morbidity among breast cancer survivors. Breast cancer cases will be limited to women age 50 years or older with a history of Stage I or node negative Stage II breast cancer, since these women are more likely to be cured of breast cancer. From 1976 to the 2004-6 follow-up cycle, we have 3344 women with breast cancer (with 561 subsequent deaths and 250 subsequent CVD events) fitting these criteria and anticipate a 10-15% increase in event rates through the 2006-8 cycle. By drawing both women with and without breast cancer from the same population with detailed updated exposures before and after cancer diagnosis, the proposed analyses address several key issues in breast cancer survivorship: the impact of competing risks on overall survival, predictors of CVD mortality to better target treatments and interventions, and the impact of changes in behavioral risk factors on overall survival. We hypothesize that early stage breast cancer survivors will be at increased CVD risk compared to women without breast cancer. Thus, health behaviors that affect CVD, breast cancer, and other chronic diseases could have a significant impact on overall survival. Clearer understanding of predictors of CVD and non- breast cancer mortality among breast cancer survivors may spur research to individualize aggressive treatments based upon a better estimation of overall risks and benefits and also facilitate targeting of behavioral interventions to improve overall survival. This application will provide important and novel information about CVD and non-breast cancer morbidity and mortality among breast cancer survivors that may spur research to individualize aggressive treatments based upon a better estimation of overall risks and benefits. Program narrative With over 2 million breast cancer survivors in the United States, we propose to evaluate the competing causes of morbidity and mortality among survivors of early stage breast cancer aged 50 years or older at diagnosis and compare these to women without breast cancer. We hypothesize that breast cancer survivors will be at increased cardiovascular risk compared to women in the general population and that intervention to improve overall survival will need to target both breast cancer and non-breast cancer related causes.